Zebra Mussels

Common Name: Zebra MusselsScientific Name: Dreissena polymorpha

Since their introduction in the late 1980s, zebra mussels (Dreissena polymorpha) have spread rapidly to all of the Great Lakes and an increasing number of inland waterways throughout the United States and Canada. As we have noticed throughout our Northern Michigan lakes, these freshwater bivalves colonize anywhere they can attach their tiny byssal threads. Many lake residents have indicated that thick colonies have attached to their docks, boat hulls, and water intake pipes. They are highly prolific reproducers; female zebra mussels can produce 1 million eggs per year!

The sheer number of zebra mussels in combination with their feeding habits has caused severe disruptions in aquatic ecosystems. Each zebra mussel is capable of filtering a liter of water per day; thus, removing almost every microscopic aquatic plant and animal (phytoplankton and zooplankton). This ecosystem disruption impacts aquatic organisms throughout the food chain, from tiny crustaceans to large trout. The effect of their feeding habits is easily discernable in water transparency data collected by volunteers, which shows that water has become clearer in lakes infested with the mussels. Increased water clarity has lead to yet another impact from zebra mussels; sunlight penetrates to greater depths and results in increased growth of rooted aquatic vegetation and bottom-dwelling algae.

Cross Village, Michigan. Photo: Kristy Beyer

While they continue to filter phytoplankton and zooplankton, they also filter other substances known as toxic contaminants. Zebra mussels have high levels of body fat, thus allowing them to accumulate ten times more PCBs and other toxic contaminants than the native mussels. Once these contaminants are stored in their bodies, they are then transferred up the food chain to their predators. Predators include some species of ducks, freshwater drum, carp, and lake sturgeon.

Zebra mussels can spread to inland waters either as veligers transported in water, or as adults attached to boat hulls, engines, bait traps, or on other items. Veligers don’t survive drying, but they can survive in any small pool of water. Adult zebra mussels can close their shells and survive drying for several days. In moist environments, they can survive out of the water even longer.What you can do to prevent the spread of this invasive species

Learn to identify zebra mussels

Inspect and remove aquatic plants and animals from boat, motor and trailer.

Rinse boat and equipment with high-pressure hot water (104° F), especially if moored for more than a day, or dry everything for at least 5 days

Report sightings of zebra mussels to Tip of the Mitt Watershed Council by calling (231) 347-1181 or by e-mail at info@watershedcouncil.org .

Declining Density in Lake MichiganOver a period of 15 years, zebra mussel densities in Lake Michigan declined from 5,200 per square meter on average to 82 animals per square meter. This decline coincides with the dramatic expansion of quagga mussel populations in the lake. (See charts below.) Similar changes have been observed in eastern Lake Erie and in Lake Ontario.